This invention relates to a method for drying drilling mud and, more particularly, to a method for drying drilling mud in a containment means in the earth's surface, in which drying is effected by passing a direct electric current through the drilling mud.
Drilling mud, which is used in the rotary drilling of oil and gas wells, consists essentially of clay and water. Normally, it is introduced into the well under high pressure through the drill pipe from which it is discharged through openings in the drill bit to cool and lubricate the bit. Other functions of the drilling mud are to control gas, oil, and water pressures in the well, thereby preventing a blowout, and to help maintain the integrity of the walls of the well.
Pressure transmitted through the drill pipe forces the drilling mud through the annular space between the drill pipe and the walls of the well, and returns it to the surface along with the cuttings produced as the bit bores into the formation. Upon reaching the surface, the drilling mud is introduced into an earthen containment means adjacent to the well site, from which it is taken for recirculation through the well. The earthen containment means is commonly known as a settling sump or reserve pit.
As much as several thousand gallons of drilling mud may be used to drill a single well, and the reserve pit will normally contain approximately that amount of mud when the well is completed.
Since drilling mud often contains valuable additives, such as barium sulfate, which is used as a weighting agent, various methods have been proposed for separating and recovering the additives from the mud for further use. However, the prior art methods often require the use of specialized and relatively expensive equipment. Representative examples of prior art drilling mud reclaiming apparatus are shown in U.S. Pat. Nos. 3,777,405 and 3,972,799. These patents both relate to portable drilling mud reclamation apparatus which employ heat and electrolytic action, respectively, for accomplishing reclamation. Because of the expense involved in practicing the prior art reclamation methods, drilling mud is discarded in many instances and simply left in the reserve pit at the drilling site. This is often the practice with wildcaters, who randomly drill oil or gas wells in a locality not known to be productive.
Due to the substantial quantity of coloidal material present in the drilling mud, evaporation of the liquid content of the mud is very slow. Moreover, depending on the consistency of the soil at the drilling site, there may be little natural seepage of liquid from the mud pit. Abandoned mud-filled pits, therefore, pose potentially serious hazards in several respects. First, if left uncovered, as is sometimes the case, rain will cause the mud to overflow the pit. The runoff, which may contain chemical additives from the drilling mud, may carry into nearby streams and rivers, resulting in their contamination. Second, abandoned mud pits pose a potential threat to the well-being of livestock which may become mired in the mud and die. Third, if the drilling site is subsequently developed for other uses, construction equipment may become bogged down in an abandoned mud pit, and result in personal injury, delays in work schedules, or the like. These last-mentioned occurrences are especially likely where the mud pit has been covered over with soil and its location is not easily detectable.
Although it has been proposed to dispose of drilling mud by procedures involving mechanical dewatering apparatus and/or trucking to a safe disposal site, these procedures are expensive and have not been widely accepted.
The development of an effective method for drying existing or new reserve drilling mud pits continues to be a highly desired objective.